Method for processing semiconductor devices in a singulated form

ABSTRACT

Improved methods and apparatus are provided for the handling and testing of semiconductor devices. One embodiment comprises a die carrier for one or more semiconductor dice having very fine pitch electrical I/O (input/output) elements. The semiconductor dice are temporarily attached to the die carrier in singulated form to enable testing the dice with conventional contact technology. The die carrier may include a flex circuit base substrate and a rigid support frame. Further embodiments comprise materials and methods for attaching the semiconductor dice to the die carrier and for providing a temporary electrical connection with the semiconductor dice during testing. Exemplary materials for providing the temporary electrical connection may comprise a conductive film or tape, a conductive or conductor-filled epoxy, resin or RTV adhesive-based materials, a water-soluble material impregnated with a conductive filler or non-reflowed solder paste.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 10/422,417,filed Apr. 23, 2003, pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the handling of semiconductordevices during processing. More particularly, the present inventionrelates to a die carrier for one or more semiconductor dice having veryfine pitch electrical I/O (input/output) elements. The semiconductordice are temporarily attached to the die carrier in singulated form toallow testing the dice with standard contact technology. The presentinvention further relates to materials and methods for temporarilyattaching the dice to the die carrier.

2. State of the Art

In semiconductor manufacturing, it is highly desirable to testsemiconductor devices for functionality prior to packaging or mountingof the devices to higher-level assemblies. By doing so, defectivedevices can be identified and eliminated without unnecessarily providingthem with further processing.

A common method for testing semiconductor devices during processingcomprises forming temporary electrical connections to the device I/Oelements with pin-type contact probes. Probe testing has beenconventionally carried out, for example, while a plurality ofsemiconductor devices are still contained within a wafer. With thisprocess, a matrix of contact probes carried by a test contactorsubstrate is forced against the I/O elements (e.g., bond pads orconductive bumps) of the semiconductor devices in the wafer, and a brieftest is conducted to determine the functionality of each device. Thewafer is subsequently singulated to provide individual semiconductordice. Any dice containing nonfunctional integrated circuits arescrapped, routed for rework if possible, or binned into a category notrequiring full functionality for less demanding applications. Theremaining dice are passed on to further processing for packaging orattaching the dice to higher-level assemblies. By using this method,semiconductor devices may be tested without substantially slowing downthe manufacturing process.

Probe testing of semiconductor devices at the wafer level, however, istypically capable of providing only a minimal measure of functionalityand does not ensure that the devices will operate suitably after finalprocessing in die form. Further, defective devices may induceundetectable failures in adjacent devices by testing them whilecoexistent on a wafer, or devices may be damaged during wafersingulation. Accordingly, the dice must be tested again after beingpackaged or otherwise incorporated into higher-level assemblies.Processing unusable semiconductor dice to this point, only to scrap themafter testing, results in a waste of production time and materials.Furthermore, as semiconductor device geometries shrink, the I/O elementsof a die become more difficult to contact and test due to tighteralignment tolerances and the need to use smaller, more fragile contactprobes.

In order to address the problems associated with testing semiconductordevices at the wafer level, manufacturers have developed methods fortesting of individual, unpackaged semiconductor dice. The methods oftenemploy temporary die carriers to hold one or more individual dice andprevent damage during testing. A prior art die carrier typicallycomprises a base portion with a cavity for housing a die and providingan electrical connection to external test circuitry. A die is placed inthe cavity circuit side down, and the die I/0 elements are biasedagainst an array of interconnects in communication with conductiveelements on the exterior of the carrier. The interconnects may take theform of bumps, pins or simple pads forming a land-grid array (LGA),depending on whether the die I/O elements are bond pads, or includestructures such as conductive bumps added for subsequent flip-chip orTAB (tape-automated-bonding) type circuit connection. Biasing the I/Oelements against the interconnects is achieved through the use of lids,clips or springs that are attached to the base portion and press on thedie. Once the die is secured, the carrier is pressed into a test socketto connect the carrier conductive elements to the external testcircuitry.

Prior art die carriers of the type discussed above are disclosed in U.S.Pat. No. 5,367,253 to Wood et al., U.S. Pat. No. 5,517,125 to Posedel etal., U.S. Pat. No. 5,767,689 to Tokuno et al. and U.S. Pat. No.6,278,286 to Farnworth et al. Although these die carriers overcome someof the problems associated with testing at the wafer level, they raiseother issues which are undesirable in the context of semiconductorprocessing. Due to their complex structure, existing die carriers may beexpensive to fabricate and include features susceptible to damage duringuse. Interconnects in the form of bumps or pins, for instance, may bedamaged or worn down by repetitive biasing against die I/O elements,especially when the interconnects are of a small size suitable forinterfacing with very fine pitch I/O elements. Likewise, the carrierconductive elements, which may comprise pins or lead-like structures,may be damaged during insertion into a test socket and do not offer theefficiency of probe-type testing. Furthermore, the lids, clips andsprings used to press on a die add cumbersome manual operations to themanufacturing process.

In view of the present state of the art, there exists a need for a diecarrier having a durable, yet simple construction and that uses animproved method for temporarily attaching one or more semiconductor diceto its interconnects.

BRIEF SUMMARY OF THE INVENTION

The present invention overcomes the deficiencies of the prior art with adie carrier that is capable of holding and protecting one or moresemiconductor dice without requiring complex or expensive structuralfeatures. The die carrier enables the use of efficientcontact-probe-type testing, without the drawbacks of testing at thewafer level. In its basic form, the die carrier comprises a planar basesubstrate having a pattern of conductive traces with attachment padscorresponding to the I/O elements of a die. The traces fan out from theI/O elements to contact pads that are spaced to interface with aconventional matrix of contact probes. The die carrier of the presentinvention does not require additional structures to hold a die in placeand bias it against the attachment pads. Instead, a die is temporarilyattached to the die carrier by an electrically conductive adhesivematerial placed over the I/O elements on the face of the die. Individualsemiconductor dice may thereby be tested for functionality withoutunduly adding to the cost or complexity of processing.

In one exemplary embodiment of the die carrier of the present invention,the base substrate of the die carrier comprises a flex circuit. Flexcircuits, as known in the art, typically comprise one or more sheets ofpolyimide or polyester material having thin, foil-like traces of metal,alloys, or other conductive materials formed on the surfaces of thesheets. This construction allows a flex circuit to bend or twist withoutbeing damaged, unlike more rigid conventional laminated circuit boards.Flex circuits, at least when formed with two circuit layers or less, arealso less expensive to produce than conventional laminated circuitboards. The low cost associated with fabricating a flex circuit makes itdesirable for use as a base substrate for the die carrier. Furthermore,the pliant nature of a flex circuit allows it to yield when forcedagainst contact probes. This characteristic reduces stress on the testequipment and improves the electrical connection with I/O elements bypressing the flex circuit towards an attached die.

In a further embodiment of the die carrier of the present invention, asupport frame is secured to the die-side surface of the base substrate.The support frame comprises a planar substrate having at least oneaperture for exposing the attachment pad area of the die carrier and atleast partially surrounding the sides of an attached die. By surroundingan adhesively attached die, the support frame helps to prevent the diefrom being damaged or inadvertently knocked off the die carrier duringhandling. When using a flex circuit as a base substrate, the supportframe adds rigidity to the die carrier while still allowing the flexcircuit to yield under the attachment pad areas. The support frame maybe secured to the die carrier with an adhesive, by press-fit elements,or by any other suitable means as known in the art.

Mechanical alignment features may further be included on the die carrierto aid in aligning the die carrier with a matrix of contact probes.According to one embodiment of the present invention, the alignmentfeatures comprise apertures or notches formed through the basesubstrate, the support frame of the die carrier, or both.

Additional embodiments of the present invention are directed to theadhesive materials and methods used for temporarily attaching a die tothe die carrier.

In one exemplary embodiment of the present invention, the adhesivematerial comprises an electrically conductive adhesive tape applied tothe die-side surface of the die carrier over the attachment pads. A dieis placed in a facedown orientation on the tape and is thereby attachedto the die carrier. The conductive properties of the tape provide anelectrical connection between the I/O elements on the die and the diecarrier attachment pads. After the completion of testing, the die may beremoved from the die carrier by simply pulling it off the tape. Suitableconductive adhesive tapes are known in the art and typically function byanisotropic, or z-axis, conduction between the sides of the tape. Thetape may further comprise a pressure-sensitive adhesive tape, which onlyconducts transverse to the plane of the tape when pressure is applied.This may be desirable when the base substrate of the die carriercomprises a flex circuit that is pressed against an attached die duringtesting.

In another exemplary embodiment of the present invention, the adhesivematerial comprises an electrically conductive liquid, gel or paste thatis applied to the die carrier attachment pads. The material maycomprise, for example, a conductive or conductor-filled epoxy, resin orroom temperature vulcanized (RTV) silicon or similar material. In someinstances, a die may be bonded to the die carrier by curing the epoxy,resin, or RTV adhesive and then using a solvent or deactivating agent tobreak the bond after the completion of testing. Alternatively, if theepoxy, resin or RTV adhesive material provided sufficient adhesion in anuncured or partially cured (B-stage) state, a die may simply be held inplace without complete curing. After testing, the die is pulled off thedie carrier and cleaned to remove residual epoxy, resin or RTV material.The liquid, gel or paste may also be comprised of a water-solublematerial that sets up with dehydration. The water-soluble material isapplied to the die carrier, and the die is placed on the material. Thewater-soluble material is then solidified by ambient or heated drying toform a bond between the die carrier and the die. When testing isfinished, the water-soluble material may simply be washed away withwater and the die removed.

In yet another exemplary embodiment of the present invention, theadhesive material may comprise a volume of solder paste. As is known inthe art, solder paste comprises fine particles of metals such as tin andlead which are suspended in a flux carrier. Conventional use of solderpaste involves heating it to reflow the particles of metal to a moltenstate and form a permanent bond between conductive elements. As used inthe present invention, solder paste is applied to the die carrierattachment pads, and the die is placed on the solder paste. The solderpaste is only heated sufficiently to drive off volatile components ofthe flux without reflowing the metal particles. In this manner, thesolder paste solidifies into a mass of metal particles entrained withindried flux material that bonds the die to the die carrier. As with theabove-described water-soluble material, the solder paste is washed awayafter testing to release the die.

Other and further features and advantages will be apparent from thefollowing detailed description of the present invention when read inconjunction with the accompanying drawings. It should be understood thatthe embodiments described are provided for illustrative and exemplarypurposes only, and that variations to, and combinations of, the severalelements and features thereof are contemplated as being within the scopeof the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, which illustrate what is currently considered to be thebest mode for carrying out the invention:

FIG. 1A shows a sectional side view of a die carrier according to thepresent invention;

FIG. 1B shows the die carrier depicted in FIG. 1A including a supportframe;

FIG. 2 shows the die carrier depicted in FIG. 1B including alignmentfeatures aligned with a probe tester;

FIG. 3A shows an exploded perspective view of a die carrier;

FIG. 3B shows a perspective view of the die carrier depicted in FIG. 3Awith the support frame and semiconductor die secured to the basesubstrate;

FIG. 4A shows a top view of a die carrier for multiple dice including asupport frame with a single aperture of a size sufficient to at leastpartially surround all of the multiple dice;

FIG. 4B shows a top view of a die carrier for multiple dice including asupport frame having multiple apertures for at least partiallysurrounding each die of the multiple dice;

FIG. 5 shows a die carrier with a conductive film or adhesive tape forattaching a semiconductor die;

FIG. 6 shows a water-soluble mask as conventionally used to holdthrough-hole electronic components;

FIG. 7 shows a schematic view of a water-soluble bond used to provide atemporary electrical connection according to the present invention;

FIG. 8A shows a schematic view of a solder paste bond used to provide atemporary electrical connection with a pad-like structure;

FIG. 8B shows a schematic view of a solder paste bond used to provide atemporary electrical connection with a conductive bump; and

FIG. 9 shows a semiconductor die bonded to a die carrier with awater-soluble material deposited around a peripheral edge of thesemiconductor die.

DETAILED DESCRIPTION OF THE INVENTION

Turning initially to the accompanying drawings, die carrier structuresand materials and methods for temporarily attaching one or moresemiconductor dice thereto are depicted to show various embodiments ofthe present invention. Common elements of the embodiments are designatedwith like reference numerals. It should be understood that the drawingsare not illustrative of actual views of any particular portion of theactual device structures, but are merely idealized schematicrepresentations which are employed to more clearly and fully depict theinvention.

FIG. 1A shows a side view of a die carrier 2 structured for useaccording to the present invention. In this embodiment, die carrier 2 isshown in a basic form comprised of a substantially planar base substrate4 configured to hold a single semiconductor die 6. Base substrate 4includes a die-side surface 8 having a pattern of conductive traces 10formed thereon. The first ends of traces 10 comprise attachment pads 12that are positioned on die-side surface 8 in locations corresponding tothe pattern of I/O elements 14, such as bond pads or redistributedexternal contact locations on die 6. The pattern of I/O elements 14 maytake the form of one or more spaced rows on the face of die 6. If I/Oelements 14 are laid out in a fine pitch pattern used with presentcircuit densities, for example, they would comprise rows of elementsspaced or pitched at intervals of about 0.5 mm or less. Of course, anyother arrangement of I/O elements on the face of a semiconductor die maybe accommodated by a die carrier according to the present invention.

I/O elements 14 are temporarily secured to attachment pads 12 by anelectrically conductive adhesive material 16. The specific features andembodiments of adhesive materials disclosed by the present invention aredescribed in further detail below. As shown in FIG. 1A, I/O elements 14are depicted as being pad-like LGA structures such as bare die bondpads. It is to be understood, however, that I/O elements 14 may alsoinclude structures such as conductive bumps added for subsequentflip-chip or TAB-type circuit connection, and that these structures maybe similarly secured by adhesive material 16.

FIG. 1A further shows that traces 10 extend from I/O elements 14 to apattern of contact pads 18 that are sufficiently spaced to interfacewith a standard matrix of contact probes 34 (FIG. 2). A standard testmatrix, for instance, may conventionally have probes spaced at a pitchof about 0.8 mm or greater. In one arrangement, contact pads 18 areformed on a back surface 20 of base substrate 4 and are electricallyconnected to the second ends of traces 10 by way of conductive vias 22.In this manner, die carrier 2 is configured to be contacted from below,as is often the approach used with conventional test equipment. Inanother arrangement, contact pads 18′ may be formed on die-side surface8 of base substrate 4, thereby allowing die carrier 2 to be contactedfrom above. It is further contemplated that in some cases, passivedevices 11 (FIG. 3A) may be included on base substrate 4 and connectedto traces 10 at points between I/O elements 14 and contact pads 18. Whentesting high-frequency semiconductor devices, for instance, the addedcircuit length from traces 10 may generate signal noise that isdetrimental to the test results. By including passive devices 11 (e.g.,capacitors, resistors or inductors), the signal noise may be reduced oreliminated.

In one presently preferred embodiment of die carrier 2, base substrate 4comprises a flex circuit formed of a core of one or more sheets ofpliant material. As used herein, the term “pliant material” refers tomaterials that enable base substrate 4 to be bent, twisted or otherwisereshaped from its substantially planar configuration, such as polyimideor polyester materials conventionally known for use in fabricating flexcircuits. Traces 10, attachment pads 12 and contact pads 18 may comprisepatterned metal or metal alloy foils formed on the surfaces of or withinthe sheets of pliant material, or may comprise one or more layers ofapplied conductive polymer materials known for use as conductors in flexcircuits. The flex circuit design allows die carrier 2 to be easilyfabricated without requiring specialized manufacturing processesassociated with the more complex structures of prior art die carriers.Furthermore, it is well known that the product life of a specificsemiconductor die layout is relatively short due to constantimprovements in technology. In the past, changing the I/O layout of adie required an expensive retooling to provide new die carriers. The lowcost of a flex circuit reduces the concerns of having to replace diecarriers to accommodate a new die I/O layout.

In some instances, however, process conditions may require basesubstrate 4 to have a more substantial construction than that offered bya flex circuit. It is, therefore, contemplated that base substrate 4 maybe formed as a rigid structure such as a laminated circuit board of, forexample, FR-4, FR-5, or BT material.

According to a further embodiment of the present invention, die carrier2 includes a support frame 24 as shown in FIG. 1B. Support frame 24comprises a planar substrate having an aperture 26 that exposes the dieattachment area of base substrate 4 and at least partially surrounds thesides of die 6. Support frame 24 is depicted in FIG. 1B as having athickness that is approximately equal to a thickness of die 6 in orderto completely surround its sides within aperture 26. Support frame 24thereby protects die 6 from being damaged or knocked off of basesubstrate 4 while being handled. Of course, it is within the scope ofthe present invention that support frame 24 may have a lesser or greaterthickness than that of die 6, if so desired. Support frame 24 may beformed of any material known for use with die carriers or othersemiconductor-type fixtures. In the case where base substrate 4 is aflex circuit, support frame 24 should be of a material sufficientlyrigid to maintain the planarity of base substrate 4 during handling andtesting. When base substrate 4 is constructed of a rigid material, themain function of support frame 24 is to protect the sides of die 6, butit may also offer additional rigidity. Plastics, metals, ceramics,laminated glass composites or other common materials would be suitablefor this purpose. Support frame 24 may be temporarily or permanentlysecured to base substrate 4 by any known means. In FIG. 1B, supportframe 24 is depicted as being secured in place by an adhesive layer 28,which may, for example, comprise a dispensed liquid or gel adhesive or atape or film segment coated on both sides with a suitable adhesive.

Die carrier 2 may also include alignment features 30 that aid itsalignment during testing. FIG. 2 shows the function of alignmentfeatures 30 when die carrier 2 is seated on a probe tester 32. Probetester 32 is schematically shown to include a matrix of contact probes34 carried by a test contactor substrate 36. Contact probes 34 areresiliently biased against contact pads 18 of die carrier 2 to formtemporary electrical connections for the testing of die 6. Probe tester32 further includes alignment pins 38 that extend outwardly from testcontactor substrate 36 to a point above contact probes 34. As shown inFIG. 2 alignment features 30, which in this embodiment are aperturespassing through base substrate 4 and support frame 24, are seated aroundalignment pins 38. In this manner, contact pads 18 of die carrier 2 areforced into alignment with contact probes 34. This ensures a goodelectrical connection will exist for testing die 6. While alignmentfeatures 30 are depicted as comprising apertures passing through basesubstrate 4 and support frame 24, it is to be understood that otherconfigurations are possible and contemplated as being within the scopeof the present invention. For instance, alignment features 30 mightcomprise notches located on the peripheral edge of die carrier 2 thatengage alignment pins 38, or may comprise elements that protrude fromdie carrier 2 and mate with holes formed in test contactor substrate 36.

FIG. 3A shows an exploded perspective view of die carrier 2 having basesubstrate 4 and support frame 24 for surrounding die 6. As depicted inFIG. 3A, base substrate 4 is configured with traces 10 fanning out fromfour rows of attachment pads 12 to four rows of conductive vias 22overlying contact pads 18 (not shown). A passive device 11 is also shownon base substrate 4 as being connected to a trace 10 for reducing oreliminating signal noise. In this embodiment of die carrier 2, alignmentfeatures 30 comprise notches formed on the peripheral edges of basesubstrate 4 and support frame 24. FIG. 3B shows support frame 24 securedto base substrate 4 and die 6 attached to die carrier 2 within aperture26.

FIGS. 3A and 3B highlight the utility of using die carrier 2 for testingof semiconductor dice having very fine pitch I/O elements. By spreadingout the location of contact pads 18 (see FIG. 1B), smaller and morefragile contact probes are not required to match up with the layout ofI/O elements 14 on die 6. Instead, conventional test equipment withconventionally sized and pitched contact probes may be utilized. FIGS.3A and 3B also highlight the benefit of using a flex circuit for basesubstrate 4. Because support frame 24 does not overlie the location ofcontact pads 18, a flex circuit base substrate 4 may yield slightly whenpressed on by contact probes 34. This reduces the stress on the testequipment. Furthermore, in embodiments of die carrier 2 where at leastsome of contact pads 18 are located under die 6, base substrate 4 willbe pushed towards I/O elements 14, thereby improving the electricalconnection through adhesive material 16.

While FIGS. 1A–3B have depicted die carrier 2 as holding a singlesemiconductor die 6, it is also contemplated that die carrier 2 may beformed to accommodate multiple dice for simultaneous testing. Basesubstrate 4 would simply be formed with attachment pads, traces andcontact pads corresponding to the I/O elements of multiple dice. Supportframe 24 may be provided with an aperture 26′ of sufficient size to atleast partially surround all the dice 6, as shown in FIG. 4A, or may beprovided with multiple apertures 26″, each aperture sized to at leastpartially surround one or more of the dice 6, as shown in FIG. 4B.Alternatively, multiple die carriers, each for holding a singlesemiconductor die, may be placed into a matrix-type fixture and loweredonto an array of sockets on a test board. Each of the die carriers couldbe directly contacted by the test equipment through the fixture, or thefixture itself could include conductive elements providing electricalcommunication between the test equipment and the die carriers.

Further advantages over the prior art result from the novel materialsand methods disclosed by the present invention for temporarily attachingsemiconductor dice to a die carrier. FIGS. 5–9 show the specificfeatures and embodiments of adhesive materials as used in conjunctionwith the above-described die carrier 2. However, it is also believedthat some of the disclosed adhesive materials have not heretofore beenused for forming a temporary electrical connection between asemiconductor die and any higher-level assembly and are, therefore, inand of themselves inventive.

In one embodiment of the present invention, the adhesive materialcomprises an electrically conductive film or adhesive tape 40. FIG. 5shows adhesive tape 40 applied to the die-side surface 8 of die carrier2 over attachment pads 12. Adhesive tape 40 electrically connectsattachment pads 12 on one side thereof to I/O elements 14 of die 6 onthe other side thereof by anisotropic, or z-axis, conduction. As shownin FIG. 5, because adhesive tape 40 only conducts in a directionperpendicular to its two sides (illustrated by arrows in adhesive tape40), a single piece of tape may be applied between attachment pads 12and I/O elements 14 without any shorting occurring between adjacentlocations. After testing, die 6 would be removed from die carrier 2 in amanner similar to that known for removing a die from a dicing frameafter wafer singulation. In this process, heat is applied to adhesivetape 40 to loosen the bond with die 6, and a vacuum chuck lifts die 6off of adhesive tape 40. When base substrate 4 comprises a flex circuit,force may also be applied to die carrier 2 underneath die 6 to assist inbreaking the bond.

Adhesive tape 40 may further comprise a pressure-sensitive z-axisconductive adhesive tape that only conducts when pressure is applied.This may be beneficial, especially when base substrate 4 comprises aflex circuit, in that adhesive tape 40 will not provide an electricalconnection until it is pressed on during testing. Die 6 will, therefore,be electrically isolated when handling die carrier 2 outside of testing,and the risk of damage to die 6 from static charges known to build up inthe processing environment will be avoided. Conductive films andadhesive tapes of the type described are known in the art and arecommercially available from vendors such as 3M Corporation of St. Paul,Minn. under the product name Z-Axis Adhesive Film 5303R-1, as well asSheldahl, Inc. of Northfield, Minn., under the product name Z-Link.

In another embodiment, the adhesive material comprises an electricallyconductive liquid, gel or paste. The liquid, gel or paste is applied toeach of the attachment pads 12 of die carrier 2, as generally shown byadhesive material 16 in FIGS. 1A and 1B. One material suitable for thisembodiment is a conductive or conductor-filled resin or epoxy.Conductive resins and epoxies have conventionally been used insemiconductor manufacturing to permanently bond die I/O elements tohigher-level assemblies. This is accomplished by curing the resins andepoxies after die attachment to form a solidified conductive bondbetween the die I/O elements and conductive elements of the higher-levelassemblies. When used in conjunction with the present invention, theresin or epoxy may be similarly cured to form a solidified conductivebond between attachment pads 12 and I/O elements 14. After testing, thebond would be broken by a solvent or deactivating agent to allow removalof die 6 from die carrier 2. The specific solvent or deactivating agentwould be based on the composition of the resin or epoxy used to bond I/Oelements 14 to attachment pads 12. A suitable solvent might comprise,for example, an alcohol-based fluid capable of breaking down the epoxyor resin in a solvent bath. When using a thermoplastic resin or epoxy,on the other hand, a deactivating agent might comprise heat applied tothe resin or epoxy after testing.

Another suitable material for this embodiment is a room temperaturevulcanized (RTV) adhesive of silicon or similar materials, an example ofwhich is commercially available from Henkel Loctite Corp. of Rocky Hill,Conn., under the product name 5421. Electrically Conductive Adhesive.The RTV adhesive may be impregnated with conductive particles such aspowdered silver, which would then provide a conductive bond betweenattachment pads 12 and I/O elements 14. RTV adhesive adheres well totin/lead coatings that may be commonly used to cover circuit elementssuch as attachment pads 12, while these adhesives are less adherent togold, which is often used for die structures such as I/O elements 14.Using an adhesive with this characteristic may simplify removal of die 6after testing because bond separation of the cured I/O adhesive would bemore likely to occur at the interface with I/O elements 14.

In an alternative to the above embodiments, if the resin, epoxy or RTVadhesive provides sufficient adhesion in an uncured or partially cured(B-stage) state, die 6 may be held in place during testing withoutcompletely curing the resin, epoxy or RTV adhesive into a solidifiedbond. After testing, die 6 could then simply be pulled off of diecarrier 2 without requiring further processing to break a solidifiedbond between I/O elements 14 and attachment pads 12. Cleaning ofresidual resin, epoxy or RTV adhesive from I/O elements 14 might berequired after separation of die 6 from die carrier 2, but this processwould be much less labor intensive than having to use a solvent ordeactivating agent to break a solidified bond.

It is also envisioned that the adhesive material in liquid, gel or pasteform may comprise a water-soluble material that sets up withdehydration. In the prior art, similar water-soluble mask materials havebeen used to hold through-hole electronic components onto circuit boardsduring wave soldering operations. FIG. 6 shows how a mask material 42 isconventionally applied in the form of a liquid, gel or paste to thesurface of a circuit board 44 along the sides of a through-holecomponent 46. Mask material 42 is then solidified by ambient or heateddrying such that component 46 is bonded to circuit board 44. The entireassembly is passed through a wave solder machine, thereby forming solderjoints 48 between the leads 50 of component 46 and through-holes 52 incircuit board 44. Mask material 42 is thereafter removed by washing itaway with water. Water-soluble mask materials used for this purpose arecommercially available from several vendors, and are typicallyformulated from polymer and/or copolymer materials mixed with an organicsolvent such as an alcohol. Contronic Devices Inc. of Huntington Beach,Calif., for instance, offers liquid- or paste-type masks under theproduct names “WSM-90T Comp Hold” and “NI Comp Hold 60LH.” KesterCompany of Des Plaines, Ill., also offers a similar water-soluble maskunder the product name TC-564-1.

These water-soluble masks are not formulated to be conductive in nature,and it is believed that they have not previously been contemplated foruse in providing temporary electrical connections. According to thepresent invention, a water-soluble material, such as the above-describedcomponent masks, is made conductive by impregnating it with a filler ofconductive material particles. This is similar to methods used formaking conductive epoxies, wherein very fine particles of silver orother conductive materials are added to provide conductive pathwaysthrough the epoxy structure.

FIG. 7 shows the structure of a water-soluble material 54 used in thepresent invention to provide a temporary electrical connection betweenattachment pads 12 of die carrier 2 and I/O elements 14 of die 6. Inthis attachment method, water-soluble material 54 is impregnated withconductive particles 56 and applied to each of attachment pads 12.Conductive particles 56 may comprise a powdered metal, such as silver orlead or any other conductive material that may be entrained withinwater-soluble material 54. I/O elements 14 of die 6 are placed intocontact with water-soluble material 54, which is subsequently dehydratedto form a solid bond securing die 6 to die carrier 2. Depending on thecomposition of water-soluble material 54, it may simply be dried overtime in the ambient environment or dried under elevated temperatures.Adjacent, mutually contacting conductive particles 56 form conductivepathways through water-soluble material 54, thereby providing atemporary electrical connection between attachment pads 12 and I/Oelements 14. When testing has been completed, water-soluble material 54is dissolved with water to release die 6 from die carrier 2.

In another embodiment of the present invention, solder paste is used toattach die 6 to die carrier 2. FIG. 8A shows the structure of a volumeof solder paste 58 acting as the adhesive material for bonding I/Oelements 14 to attachment pads 12. As known in the art, solder paste 58comprises fine metal particles or spheres 60, such as tin and lead,suspended in a flux carrier 62. Solder pastes of this type arecommercially available from vendors such as Kester Company of DesPlaines, Ill. Flux carrier 62 initially comprises a semifluid media,typically resin-based with a volatile organic solvent. In the presentattachment method, solder paste 58 is applied to each of attachment pads12, and I/O elements 14 of die 6 are placed on top of solder paste 58.Solder paste 58 is only heated to a point where the volatile solventcomponent of flux carrier 62 evaporates without any melting of metalspheres 60. In this manner, flux carrier 62 sets up into a solidifiedstructure that entrains metal spheres 60 and is adhered to attachmentpads 12 and I/O elements 14. Adjacent, mutually contacting metal spheres60 form conductive pathways through solder paste 58, thereby providing atemporary electrical connection between attachment pads 12 and I/Oelements 14. As with the above-described water-soluble material 54, oncetesting is complete, solder paste 58 is washed away to release die 6from die carrier 2. The wash medium may be water or some other solvent,such as alcohol, suitable for dissolving the composition of flux carrier62.

FIG. 8B shows an embodiment using solder paste 58 as an adhesivematerial wherein I/O elements 14 are not pad-like structures, but rathercomprise conductive bumps 64 that are used for flip-chip or TABconnection. Under this embodiment, conductive bumps 64 are pressed downinto solder paste 58 such that metal spheres 60 and flux carrier 62 areforced up around the sides of conductive bumps 64. The heating of fluxcarrier 62 into a solidified structure is then carried out in the samemanner as described with pad-like I/O elements.

Although the present invention has been described with respect to theillustrated embodiments, various additions, deletions and modificationsare contemplated as being within its scope. For instance, die carrier 2may have a perimeter shape other than rectangular, or may be dimensionedto fit into standardized handling trays used for transportation of dicebetween equipment locations. Likewise, while support frame 24 has beendepicted in FIGS. 1A–3B as having a specific size in relation to basesubstrate 4, any other dimensions are possible. Support frame 24 mayextend beyond the edges of base substrate 4 or might be comprised ofseparate elements attached to isolated portions of base substrate 4.

Furthermore, as stated above, the adhesive materials and methodsdisclosed by the present invention may be used for providing a temporaryelectrical connection between electronic devices other than whenattaching a semiconductor die to a die carrier. It is also contemplatedthat an adhesive material may be used for temporarily attaching asemiconductor die to the die carrier without providing an electricalconnection. For example, an adhesive tape may simply be placed over thesupport frame aperture to hold or assist in holding a die in placeduring testing. As shown by dashed lines in FIG. 1B, a section ofadhesive tape 70 is placed across aperture 26 in support frame 24 andholds die 6 in contact with attachment pads 12.

Likewise, the above-described water-soluble mask material 42 may be usedwithout any conductive filler and placed around the periphery of die 6to hold I/O elements 14 against attachment pads 12 on base substrate 4during testing, as shown in FIG. 9. Similar to the above-described wavesoldering operations, mask material 42 is solidified by ambient orheated drying such that die 6 is bonded to base substrate 4. Die 6 istested, and mask material 42 is thereafter removed by washing it awaywith water.

The scope of the present invention is, therefore, indicated by theappended claims, rather than the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

1. A method for temporarily conductively bonding circuit assembliescomprising: providing an electronic device including a first conductiveelement; providing a substrate including a second conductive element;applying a conductive material including an aqueous solvent and a watersoluble material impregnated with a conductive filler comprisingdiscrete particles to at least one of the first conductive element andthe second conductive element; dehydrating the conductive material to adegree sufficient to provide an at least partially solidified bondbetween the first conductive element and the second conductive elementwithout substantially removing or degrading the water-soluble material;and removing the conductive material to release the at least oneelectronic device from the substrate.
 2. The method of claim 1, furthercomprising forming the conductive filler of the water-soluble materialfrom discrete particles of a metal or metal alloy.
 3. The method ofclaim 1, further comprising selecting the water-soluble material tocomprise a polymer or copolymer-based material.
 4. The method of claim1, wherein providing an electronic device comprises providing asemiconductor die.
 5. The method of claim 4, further comprising probinga third conductive element on the substrate to test a functional aspectof the semiconductor die.
 6. A method for temporarily conductivelybonding circuit assemblies comprising: providing an electronic deviceincluding a first conductive element; providing a substrate including asecond conductive element; applying a solder paste having discreteparticles of a metal or metal alloy entrained within a soluble fluxcarrier to at least one of the first conductive element and the secondconductive element; heating the solder paste to provide an at leastpartially solidified solder paste structure comprising the discreteparticles of a metal or metal alloy entrained within a remaining,non-solvent portion of the soluble flux carrier, wherein the at leastpartially solidified solder paste structure forms a bond between thefirst conductive element and the second conductive element; and removingthe solder paste to release the at least one electronic device from thesubstrate.
 7. The method according to claim 6, wherein heating thesolder paste comprises driving off volatiles in the soluble flux carrierwhile maintaining the particles of a metal or metal alloy in a solidstate within a matrix of remaining material of the soluble flux carrier.8. The method of claim 6, wherein providing an electronic devicecomprises providing a semiconductor die.
 9. The method of claim 6,further comprising probing a third conductive element on the substrateto test a functional aspect of the electronic device.